Tryptamine-based human β3-adrenergic receptor agonists. Part 1: SAR studies of the 7-position of the indole ring

2D-QSAR and 3D-QSAR/CoMSIA Studies on a Series of (R)-2-((2-(1H-Indol-2-yl)ethyl)amino)-1-Phenylethan-1-ol with Human β₃-Adrenergic Activity

The β₃ adrenergic receptor is raising as an important drug target for the treatment of pathologies such as diabetes, obesity, depression, and cardiac diseases among others. Several attempts to obtain selective and high affinity ligands have been made. Currently, Mirabegron is the only available drug on the market that targets this receptor approved for the treatment of overactive bladder. However, the FDA (Food and Drug Administration) in USA and the MHRA (Medicines and Healthcare products Regulatory Agency) in UK have made reports of potentially life-threatening side effects associated with the administration of Mirabegron, casting doubts on the continuity of this compound. Therefore, it is of utmost importance to gather information for the rational design and synthesis of new β₃ adrenergic ligands. Herein, we present the first combined 2D-QSAR (two-dimensional Quantitative Structure-Activity Relationship) and 3D-QSAR/CoMSIA (three-dimensional Quantitative Structure-Activity Relationship/Comparative Molecular Similarity Index Analysis) study on a series of potent β₃ adrenergic agonists of indole-alkylamine structure. We found a series of changes that can be made in the steric, hydrogen-bond donor and acceptor, lipophilicity and molar refractivity properties of the compounds to generate new promising molecules. Finally, based on our analysis, a summary and a regiospecific description of the requirements for improving β₃ adrenergic activity is given.

β(3)-Adrenoceptor agonists and (antagonists as) inverse agonists history, perspective, constitutive activity, and stereospecific binding

β(3)-Adrenergic receptor (β(3)-AR) is expressed in several tissues and is considered a drug target for the treatment of several pathologies such as obesity, type 2 diabetes, cachexia, metabolic syndrome, heart failure, anxiety and depressive disorders, preterm labor, overactive bladder, control colon motility, and of coadjuvants in colon cancer therapy. It is a seven-transmembrane domain (7TD) G-protein coupled receptor and is usually coupled to a Gs-protein (Gi-protein in very few cases), and its stimulation increases the production of cAMP. A lot of β(3)-AR agonists have been uncovered and extensively characterized. Conversely, very little is known about β(3)-AR inverse agonists that would suppress the agonist-independent activity (constitutive activity) of the receptor by stabilizing it in its inactive state. This chapter attempts to outline (a) the importance of the β(3)-AR as a therapeutic target through the disquisition of its role in human health (physiology) and disease (pathology); (b) the description of β(3)-AR structure [amino acid sequence and 7TD organization]; (c) the medicinal chemistry of β(3)-AR: 7TD amino acid-ligand specific interactions, β-adrenoreceptor subtype selectivity, stereospecific interactions and biological activity relationships, inverse agonism and blockage of β(3)-adrenoceptor constitutive activity; and (d) β(3)-AR inverse agonists. The detailed procedure to prepare and assess the biological activity/selectivity of the more potent and selective β(3)-AR inverse agonists (SP-1e and SP-1g) up to now known is also described.

Comparative 3D QSAR study on β(1)-, β(2)-, and β(3)-adrenoceptor agonists

A quantitative structure–activity relationship study of tryptamine-based derivatives of β₁-, β₂-, and β₃-adrenoceptor agonists was conducted using comparative molecular field analysis (CoMFA). Correlation coefficients (cross-validated r²) of 0.578, 0.595, and 0.558 were obtained for the three subtypes, respectively, in three different CoMFA models. All three CoMFA models have different steric and electrostatic contributions, implying different requirements inside the binding cavity. The CoMFA coefficient contour plots of the three models and comparisons among these plots provide clues regarding the main chemical features responsible for the biological activity variations and also result in predictions which correlate very well with the observed biological activity. Based on the analysis, a summary regeospecific description of the requirements for improving β-adrenoceptor subtype selectivity is given.

Stereospecific synthesis and bio-activity of novel beta(3)-adrenoceptor agonists and inverse agonists

Since it is widely distributed into the body, beta(3)-adrenoceptor is becoming an attractive target for the treatment of several pathologies such as obesity, type 2 diabetes, metabolic syndrome, cachexia, overactive bladder, ulcero-inflammatory disorder of the gut, preterm labour, anxiety and depressive disorders, and heart failure. New compounds belonging to the class of arylethanolamines bearing one or two stereogenic centres were prepared in good yields as racemates and optically active forms. They were, then, evaluated for their intrinsic activity towards beta(3)-adrenoceptor and their affinity for beta(1)- and beta(2)-adrenergic receptors. Stereochemical features were found to play a crucial role in determining the behaviour of such compounds. In particular, alpha-racemic, (alphaR)- and (alphaS)-2-{4-[2-(2-hydroxy-2-phenylethylamino)ethyl]phenoxy}-2- methylpropanoic acid, (alpha-rac, beta-rac)-, (alphaR, betaS)- and (alphaR, betaR)- 2-{4-[2-(2-hydroxy-2-phenylethylamino)ethyl]phenoxy}propanoic acid were found to be endowed with beta(3)-adrenoceptor agonistic activity. Whereas, (alphaS, betaS)- and (alphaS, betaR)-2-{4-[2-(2-hydroxy-2-phenylethylamino)ethyl]phenoxy}propanoic acid behaved as beta(3)-adrenoceptor inverse agonists. Such compounds showed no affinity for beta(1)- and beta(2)-adrenergic receptor, respectively. Thus, resulting highly selective beta(3)-adrenoceptor ligands.

Tryptamine-based human beta3-adrenergic receptor agonists. Part 2: SAR of the methylene derivatives

A series of tryptamine derivatives with modified sulfonamide were designed, synthesized, and evaluated for their ability to stimulate cAMP accumulation in CHO cells expressing the cloned human beta3-adrenergic receptor (AR). For this series of compounds, our objective was to symmetrize the alpha-position of the tryptamine moiety maintaining its activity and reducing the cost of production. Compound 11h, having m-aminobenzene, exhibited excellent agonistic activity for beta3-AR with excellent subtype selectivity.

Tryptamine-based human β3-adrenergic receptor agonists. Part 3: Improved oral bioavailability via modification of the sulfonamide moiety

The continued SAR investigation of tryptamine-based human beta(3)-adrenergic receptor (AR) agonists is reported. Prior efforts resulted in the identification of 2 as a potent beta(3)-AR agonist. Further modification of the left side arylsulfonamide portion in 2 provided compounds with good cell permeability, which have potent agonistic activity for beta(3)-AR. Cinnamylamine analog 16i exhibited an excellent agonistic profile in vitro and good oral bioavailability in rats.